1. Field of the Invention
The present invention relates to a cathode ray tube having an electron gun which is provided with an indirectly heated cathode structures and more particularly to the electrode structure of the indirectly heated cathode structure.
2. Description of the Related Art
A cathode ray tube used in a television receiver set, a display tube or the like has the high-definition image reproducibility and hence, the cathode ray tube has been popularly used as a display means for various information processing equipments.
This type of cathode ray tube is formed of an evacuated envelope which includes a panel portion forming a phosphor screen by applying phosphor to an inner surface thereof, a neck portion housing an electron gun which has a plurality of electrodes and focuses and accelerates electron beams generated by an electron beam generating portion constituted of an indirectly heated cathode structure, a control electrode and an acceleration electrode and irradiates the electron beams to the phosphor screen, and a funnel portion connecting the panel portion and the neck portion and exteriorly mounting a deflection yoke which scans the electron beams emitted from the electron gun on the phosphor screen thereon.
FIG. 5 is a cross-sectional view for explaining the constitution of the indirectly heated cathode structure. In the drawing, the indirectly heated cathode structure 21 includes a bead support 22, an eyelet 23, a heater support 24, a heater 25, a substrate metal 27 which holds an electron emitting material layer 26, a cathode support sleeve 28 and a cathode disc 29.
The indirectly heated cathode structure 21 is fixed to a multiform glass 20 by the eyelet 23 and the bead support 22. Further, the heater 25 housed in the inside of the cathode support sleeve 28 has end portions (leg portions) thereof fixed to the heater support 24 by welding.
FIG. 6A, 6B are an explanatory view showing the constitution of the heater 25 shown in FIG. 5, wherein FIG. 6A is a side view of the heater 25 and FIG. 6B is an enlarged cross-sectional view of a portion A in FIG. 6A. In these drawings, the heater 25 is formed by applying an alumina insulation film 32 to a tungsten core 31 which is formed by spirally winding a coil, by applying tungsten fine powder 33 to a surface of the alumina insulation film 32, and by blackening the tungsten fine powder 33. This blackening treatment is performed for enhancing the efficiency of the irradiation of radiation heat from the heater 25 thus lowering a temperature of a heater 25 whereby the reliability is enhanced.
In FIG. 6A, numeral 34 indicates a heater leg portion which has a triplicate winding structure of the tungsten core 31 shown in FIG. 6B, numeral 35 indicates a duplicate spiral forming portion (a heater main portion), numeral 36 indicates a surface blackening treatment portion using the tungsten fine powder 33 shown in FIG. 6B, numeral 37 indicates an alumina coating portion, numeral 38 indicates an alumina non-coating portion, and numeral 39 indicates a molybdenum wire dissolved mark (a hollow portion). This type of indirectly heated cathode structure is disclosed in following patent literature 2 and patent literature 3 and the like.
Patent literatures 1 disclose the method for manufacturing the indirect cathode sleeve. A cathode sleeve consist of a bimetal which consist of a Nickel-Chrome alloy at an inside surface of the cathode sleeve and a Nickel alloy at an outside surface of the cathode sleeve    Patent literature 1: Japanese Unexamined Patent Publication Hei7(1995)-182965 which corresponds to U.S. Pat. No. 5,569,391.    Patent literature 2: Japanese Unexamined Patent Publication Hei11(1995)-354041 which corresponds to U.S. Pat. No. 6,492,768.    Patent literature 3: Japanese Unexamined Patent Publication 2002-93335 which corresponds to U.S. Pat. No. 6,552,479.
In the indirectly heated cathode structure of the cathode ray tube having such a constitution, with respect to the heating heater, the electric resistance of the leg portion of the heater becomes low due to the triplicate winding structure and hence, a heat value of the leg portion becomes small and the heater power concentrates on the duplicate spiral forming portion whereby the power consumption can be reduced. However, when the multiplex coil winding is merely applied to the heater leg portion, the electric resistance reduction effect is still small and hence, there exists a limit with respect to the reduction of power consumption of the heater.
Further, there has been also known a related art which proposes the constitution in which the power consumption is realized by blackening an inner wall surface of a cathode sleeve of an indirectly heated cathode structure. However, there has been known no related art which discloses or takes into an account the constitution which can reduce the power consumption positively thus realizing the low power consumption while enhancing the various electrical characteristics by improving the electrode structure of the indirectly heated cathode structure and the structure of the heated heater.
Further, recently, from a viewpoint of power saving, the low power consumption has been further strongly requested. This demand for the low power consumption constitutes one of contemporary critical issues and the significance thereof is steadily increasing. To explain the current actual power consumption state of the cathode ray tube, the power consumption of a monitor set is approximately 100W, wherein the power consumption of the indirectly heated cathode amounts to 2 to 4% of the power consumption of the monitor set.
Further, with respect to a heating heater of three-electron-gun type which is generally adopted by the cathode ray tube or the like, the heater having the specification in which the rating of the heater is 6.3V–300 mA (one electron gun: 0.63 W per one heater) is popularly used and hence, the sufficient power saving has not been realized.
Accordingly, the present invention has been made to solve the above-mentioned drawbacks of the related art and it is an object of the present invention to provide a cathode ray tube having an electron gun provided with an indirectly heated cathode structure which can reduce the power consumption of a heater by decreasing the temperature elevation of respective electrodes which constitute the indirectly heated cathode structure.